1. Technical Field
The present invention relates to technology for a fuel cell separator, a method of manufacturing a fuel cell separator, and a fuel cell.
2. Related Art
A typical fuel cell comprises an electrolyte film, a pair of electrodes (an anode and a cathode) each comprising a catalyst layer and a diffusion layer, and a pair of fuel cell separators (an anode fuel cell separator and a cathode fuel cell separator) that sandwich the electrodes. During power generation by the fuel cell, in the case where the anode gas supplied to the anode is hydrogen gas and the cathode gas supplied to the cathode is oxygen gas, a reaction that produces hydrogen ions and electrons occurs at the anode, and the hydrogen ions pass though the electrolyte film to the cathode, while the electrons flow through an external circuit and reach the cathode. At the cathode, a reaction occurs in which the hydrogen ions, the electrons and the oxygen gas react together to produce water, and energy is emitted.
FIG. 1 is a schematic representation of the top view of a typical fuel cell separator used in a fuel cell. FIG. 2 is a schematic cross-sectional view of the fuel cell separator along the line A-A shown in FIG. 1. As shown in FIGS. 1 and 2, the fuel cell separator 1 comprises reaction gas inlets 11a and 11b, protruding ribs 12 that form a gas flow passage 10, reaction gas outlets 13a and 13b, and a sealing section 14. A reaction gas used during power generation by the fuel cell is introduced, for example, via the reaction gas inlet 11a, flows through the gas flow passage 10, and is discharged through the reaction gas outlet 13a. 
The gas flow passage 10 functions not only as a passage for supplying the reaction gas to the electrode, but also as a drainage passage for draining the moisture produced during power generation by the fuel cell to a location outside the fuel cell system. Accordingly, if the drainage performance of the fuel cell separator 1 (and particularly the gas flow passage 10) is poor, then the moisture produced during power generation may accumulate within the gas flow passage 10, hindering supply of the reaction gas. As a result, the fuel cell separator 1 is usually subjected to a hydrophilic treatment in order to improve the drainage performance of the gas flow passage 10.
FIG. 3 is a series of diagrams describing a method of manufacturing a hydrophilically treated fuel cell separator. A fuel cell separator base material 16 is formed by mixing together a carbon material and a binder resin, and then pouring the resulting mixture into a mold and conducting press molding. The fuel cell separator base material 16 comprises a gas flow passage 10, ribs 12, and a sealing section 14.
As shown in FIG. 3, the fuel cell separator base material 16 is first subjected to shot blasting. Shot blasting is a technique in which particles of alumina or the like are blown at high-speed at the surface of the fuel cell separator base material 16, thereby abrading the surface of the fuel cell separator base material 16. Shot blasting removes the binder resin layer that exists at the surface of the fuel cell separator base material 16, and is able to reduce the contact resistance (the electrical resistance).
Subsequently, the shot blasted fuel cell separator base material 16 is washed and dried, and then subjected to a hydrophilic treatment, thereby forming a hydrophilically treated surface on the gas flow passage 10, the ribs 12 and the sealing section 14. Examples of suitable hydrophilic treatments include conventional methods such as fluorine gas treatments and plasma treatments. Following formation of the hydrophilically treated surface, the fuel cell separator base material 16 is washed and dried, yielding a fuel cell separator 1.
For example, Japanese Patent Laid-Open Publication No. 2005-339846 and Japanese Patent Laid-Open Publication No. 2003-109619 disclose fuel cell separators in which the fuel cell separator base material is subjected to a hydrophilic treatment to form a hydrophilically treated surface, and the hydrophilically treated surface formed on the top surface of the ribs is then removed.
However, in the fuel cell separators of these Japanese Patent Laid-Open Publications No. 2005-339846 and No. 2003-109619, a hydrophilically treated surface (or water repellent surface) is also formed on the sealing section of the fuel cell separator. This sealing section is the region that is bonded with an adhesive or the like during bonding of the fuel cell separators, the fuel cell separator and a gasket, or the fuel cell separator and a sealing plate. The hydrophilically treated surface formed on the sealing section inhibits polymerization with the adhesive, causing a reduction in the adhesive strength between the sealing section and the adhesive.
Particularly in the case of hydrophilic treatments conducted by fluorine gas treatment, if residual fluorine groups exist at the surface of the fuel cell separator sealing section, then the sealing section inhibits polymerization with the adhesive, causing a reduction in the adhesive strength between the sealing section and the adhesive.
Residual fluorine groups at the surface of the fuel cell separator sealing section can usually be partially removed by washing with water, but removal of the fluorine groups to a level that ensures favorable adhesion with adhesives is not always possible.
Although not related to the removal of the hydrophilically treated surface (or the fluorine groups) from a sealing section, Japanese Patent Laid-Open Publication No. 2004-158346 discloses a method of removing a release agent adhered to a fuel cell separator by irradiation with a laser.
Furthermore, although not related to the removal of the hydrophilically treated surface (or the fluorine groups) from a sealing section, Japanese Patent Laid-Open Publication No. 2003-282084 discloses a method of using shot blasting to selectively remove only the resin layer (the binder resin layer) on the top surfaces of the ribs.
However, the method of Japanese Patent Laid-Open Publication No. 2004-158346 also removes the hydrophilically treated surface from the gas flow passage of the fuel cell separator, meaning the drainage properties of the fuel cell separator tend to deteriorate. Furthermore, in the method of Japanese Patent Laid-Open Publication No. 2003-282084, the hydrophilically treated surface of the sealing section is not removed at all, meaning the adhesive strength at the sealing section cannot be ensured.